| 1. |
- Hammarberg, Susanna, et al.
(författare)
-
High resolution strain mapping of a single axially heterostructured nanowire using scanning X-ray diffraction
- 2020
-
Ingår i: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 13:9, s. 2460-2468
-
Tidskriftsartikel (refereegranskat)abstract
- Axially heterostructured nanowires are a promising platform for next generation electronic and optoelectronic devices. Reports based on theoretical modeling have predicted more complex strain distributions and increased critical layer thicknesses than in thin films, due to lateral strain relaxation at the surface, but the understanding of the growth and strain distributions in these complex structures is hampered by the lack of high-resolution characterization techniques. Here, we demonstrate strain mapping of an axially segmented GaInP-InP 190 nm diameter nanowire heterostructure using scanning X-ray diffraction. We systematically investigate the strain distribution and lattice tilt in three different segment lengths from 45 to 170 nm, obtaining strain maps with about 10−4 relative strain sensitivity. The experiments were performed using the 90 nm diameter nanofocus at the NanoMAX beamline, taking advantage of the high coherent flux from the first diffraction limited storage ring MAX IV. The experimental results are in good agreement with a full simulation of the experiment based on a three-dimensional (3D) finite element model. The largest segments show a complex profile, where the lateral strain relaxation at the surface leads to a dome-shaped strain distribution from the mismatched interfaces, and a change from tensile to compressive strain within a single segment. The lattice tilt maps show a cross-shaped profile with excellent qualitative and quantitative agreement with the simulations. In contrast, the shortest measured InP segment is almost fully adapted to the surrounding GaInP segments. [Figure not available: see fulltext.].
|
|
| 2. |
- Alcer, David, et al.
(författare)
-
Comparison of Triethylgallium and Trimethylgallium Precursors for GaInP Nanowire Growth
- 2021
-
Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 258:2
-
Tidskriftsartikel (refereegranskat)abstract
- Nanowire (NW) arrays containing a top segment of GaxIn1–xP are investigated, comparing NWs grown using two different Ga precursors, trimethylgallium (TMGa) and triethylgallium (TEGa). TMGa is the precursor commonly used for the particle-assisted vapor–liquid–solid (VLS) growth of GaxIn1–xP NWs. However, it shows inefficient pyrolysis at typical NW growth conditions. The use of the alternative precursor TEGa is investigated by making a direct comparison between NWs grown using TEGa and TMGa at otherwise identical growth conditions. Growth rates, resulting NW materials composition, and time-resolved photoluminescence (TRPL) lifetimes are investigated. With increasing Ga content of the NWs, the TRPL lifetimes decrease, indicating trap states that are associated with GaP. Somewhat longer TRPL lifetimes for the samples grown using TEGa indicate a lower concentration of deep trap states. For doped NWs, it is found that the strong effect of the p-type dopant diethylzinc (DEZn) on the NW composition, observed for GaxIn1–xP NWs grown using TMGa, is absent when using TEGa.
|
|
| 3. |
- Alcer, David, et al.
(författare)
-
Processing and characterization of large area InP nanowire photovoltaic devices
- 2023
-
Ingår i: Nanotechnology. - 0957-4484. ; 34:29
-
Tidskriftsartikel (refereegranskat)abstract
- III−V nanowire (NW) photovoltaic devices promise high efficiencies at reduced materials usage. However, research has so far focused on small devices, mostly ≤1 mm2. In this study, the upscaling potential of axial junction InP NW photovoltaic devices is investigated. Device processing was carried out on a full 2″ wafer, with device sizes up to 1 cm2, which is a significant increase from the mm-scale III−V NW photovoltaic devices published previously. The short-circuit current density of the largest 1 cm2 devices, in which 460 million NWs are contacted in parallel, is on par with smaller devices. This enables a record power generation of 6.0 mW under AM1.5 G illumination, more than one order of magnitude higher than previous III−V NW photovoltaic devices. On the other hand, the fill factor of the larger devices is lower in comparison with smaller devices, which affects the device efficiency. By use of electroluminescence mapping, resistive losses in the indium tin oxide (ITO) front contact are found to limit the fill factor of the large devices. We use combined light-beam induced current (LBIC) and photoluminescence (PL) mapping as a powerful characterization tool for NW photovoltaic devices. From the LBIC and PL maps, local defects can be identified on the fully processed devices.
|
|
| 4. |
- Alcer, David, et al.
(författare)
-
Vertically Processed GaInP/InP Tandem-Junction Nanowire Solar Cells
- 2024
-
Ingår i: ACS Applied Nano Materials. - 2574-0970. ; 7:2, s. 2352-2358
-
Tidskriftsartikel (refereegranskat)abstract
- We present vertically processed photovoltaic devices based on GaInP/InP tandem-junction III-V nanowires (NWs), contacting approximately 3 million NWs in parallel for each device. The GaInP and InP subcells as well as the connecting Esaki tunnel diode are all realized within the same NW. By processing GaInP/InP tandem-junction NW solar cells with varying compositions of the top junction GaInP material, we investigate the impact of the GaInP composition on the device performance. External quantum efficiency (EQE) measurements on devices with varying GaInP composition provide insights into the performance of the respective subcells, revealing that the GaInP subcell is current-limiting for all devices. I-V measurements under AM1.5G illumination confirm voltage addition of the subcells, resulting in an open-circuit voltage of up to 1.91 V. However, the short-circuit current density is low, ranging between 0.24 and 3.44 mA/cm2, which leads to a resulting solar conversion efficiency of up to 3.60%. Our work shows a path forward toward high-efficiency NW photovoltaics and identifies critical issues that need improvement.
|
|
| 5. |
- Barrigón, Enrique, et al.
(författare)
-
Light current-voltage measurements of single, as-grown, nanowire solar cells standing vertically on a substrate
- 2020
-
Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 78
-
Tidskriftsartikel (refereegranskat)abstract
- Nanowire based solar cells hold promise for terrestrial and space photovoltaic applications. However, to speed-up and further continue with nanowire solar cell development, quick and reliable characterization tools capable of evaluating single nanowire performance of nanowires still standing on the substrate are necessary. Here, we present the use of a light emitting diode (LED) based setup, which combined with a nanoprobe system inside a scanning electron microscope, enables on-wafer, single, nanowire solar cell optoelectronic characterization. In particular, we study the I–V characteristics of single nanowire solar cells under in situ illumination and correlate the results with those of electron beam induced current measurements. Further, the LED setup enables the study of nanowire solar cell under varied incident power. We believe that this approach will enable rapid development of single and tandem nanowire based solar cells as well as other nanowire based optoelectronic devices.
|
|
| 6. |
- Barrigón, Enrique, et al.
(författare)
-
Unravelling processing issues of nanowire-based solar cell arrays by use of electron beam induced current measurements
- 2020
-
Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 71
-
Tidskriftsartikel (refereegranskat)abstract
- III-V vertical nanowire arrays have great potential for next generation photovoltaics. Development towards high performing nanowire solar cells, which consist of a parallel connection of millions of single nanowire solar cells, requires a fast characterization technique that establishes a link between device performance and device processing. In this work, we use electron beam induced current measurements to characterize fully processed InP nanowire array solar cells at the nanoscale. Non-functional areas on fully processed devices can be quickly identified and processing induced effects on device performance can be clearly distinguished from those arising from nanowire growth. We identify how limiting factors on device performance are related to the processing procedures and provide a path to improve device performance further. In this way, electron beam induced current measurements become an essential tool for nanowire solar cell efficiency optimization, providing fast and useful information at the nanoscale and thus enabling up-scaling of the technology.
|
|
| 7. |
- Chayanun, Lert, et al.
(författare)
-
Direct Three-Dimensional Imaging of an X-ray Nanofocus Using a Single 60 nm Diameter Nanowire Device
- 2020
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 20:11, s. 8326-8331
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoscale X-ray detectors could allow higher resolution in imaging and diffraction experiments than established systems but are difficult to design due to the long absorption length of X-rays. Here, we demonstrate X-ray detection in a single nanowire in which the nanowire axis is parallel to the optical axis. In this geometry, X-ray absorption can occur along the nanowire length, while the spatial resolution is limited by the diameter. We use the device to make a high-resolution 3D image of the 88 nm diameter X-ray nanofocus at the Nanomax beamline, MAX IV synchrotron, by scanning the single pixel device in different planes along the optical axis. The images reveal fine details of the beam that are unattainable with established detectors and show good agreement with ptychography.
|
|
| 8. |
- Eriksson, Axl, et al.
(författare)
-
Synthesis of Well-Ordered Functionalized Silicon Microwires Using Displacement Talbot Lithography for Photocatalysis
- 2024
-
Ingår i: ACS Omega. - 2470-1343. ; 9:18, s. 20623-20628
-
Tidskriftsartikel (refereegranskat)abstract
- Metal-assisted chemical etching (MACE) is a cheap and scalable method that is commonly used to obtain silicon nano- or microwires but lacks spatial control. Herein, we present a synthesis method for producing vertical and highly periodic silicon microwires, using displacement Talbot lithography before wet etching with MACE. The functionalized periodic silicon microwires show 65% higher PEC performance and 2.3 mA/cm2 higher net photocurrent at 0 V compared to functionalized, randomly distributed microwires obtained by conventional MACE at the same potentials.
|
|
| 9. |
- Hammarberg, Susanna, et al.
(författare)
-
Fast nanoscale imaging of strain in a multi-segment heterostructured nanowire with 2D Bragg ptychography
- 2024
-
Ingår i: Journal of Applied Crystallography. - 0021-8898. ; 57, s. 60-70
-
Tidskriftsartikel (refereegranskat)abstract
- Developing semiconductor devices requires a fast and reliable source of strain information with high spatial resolution and strain sensitivity. This work investigates the strain in an axially heterostructured 180 nm-diameter GaInP nanowire with InP segments of varying lengths down to 9 nm, simultaneously probing both materials. Scanning X-ray diffraction (XRD) is compared with Bragg projection ptychography (BPP), a fast single-projection method. BPP offers a sufficient spatial resolution to reveal fine details within the largest segments, unlike scanning XRD. The spatial resolution affects the quantitative accuracy of the strain maps, where BPP shows much-improved agreement with an elastic 3D finite element model compared with scanning XRD. The sensitivity of BPP to small deviations from the Bragg condition is systematically investigated. The experimental confirmation of the model suggests that the large lattice mismatch of 1.52% is accommodated without defects.
|
|
| 10. |
- Hrachowina, Lukas, et al.
(författare)
-
Development and characterization of photovoltaic tandem-junction nanowires using electron-beam-induced current measurements
- 2022
-
Ingår i: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 15:9, s. 8510-8515
-
Tidskriftsartikel (refereegranskat)abstract
- Nanowires have many interesting properties that are of advantage for solar cells, such as the epitaxial combination of lattice-mismatched materials without plastic deformation. This could be utilized for the synthesis of axial tandem-junction nanowire solar cells with high efficiency at low material cost. Electron-beam-induced current measurements have been used to optimize the performance of single-junction nanowire solar cells. Here, we use electron-beam-induced current measurements to break the barrier to photovoltaic tandem-junction nanowires. In particular, we identify and subsequently prevent the occurrence of a parasitic junction when combining an InP n—i—p junction with a tunnel diode. Furthermore, we demonstrate how to use optical and electrical biases to individually measure the electron-beam-induced current of both sub-cells of photovoltaic tandem-junction nanowires. We show that with an applied voltage in forward direction, all junctions can be analyzed simultaneously. The development of this characterization technique enables further optimization of tandem-junction nanowire solar cells.
|
|
